Influences of grain size on the deformation behavior of a twinning- induced plasticity metastable β titanium alloy

The influences of grain size on the deformation behavior of a metastable beta-type Ti-12Mo (wt%) alloy has been investigated by using uniaxial tensile testing, scanning electron microscopy and electron backscatter diffraction. The results reveal that the twinning-induced plasticity (TWIP) effect mediated by {332} < 113 > beta twins occurs in this alloy when its mean grain size (d0) ranges from 49 to 104 pm, leading to pronounced work hardening behavior and a large uniform elongation (> 25%). Furthermore, there is a Hall-Petch re-lationship between the yield strength and d0 for this d0 range, with a Hall-Petch coefficient higher than that expected for pure slip deformation. However, when this alloy is in a state with heterogeneous grain structures and smaller grain sizes (d0 similar to 30 pm), only a very limited volume fraction (< 1.8%) of {332} < 113 > beta twins occurs and these twins prefer to nucleate in large grains (> similar to 40 pm), but they can propagate into rather small grains (< similar to 25 pm). In such a state, the Ti-12Mo alloy has a high yield strength (1025 MPa) but does not exhibit any sign of work hardening, i.e., the TWIP effect is absent. Based on the alpha-assisted {332} < 113 > beta twinning mechanism, the effects of grain size on the {332} < 113 > beta twinning and yield strength are discussed in terms of its role in affecting the stress-induced beta ->alpha martensitic transformation. (c) 2022 Elsevier B.V. All rights reserved.

Automated summary

The influences of grain size on the deformation behavior of a metastable beta-type Ti-12Mo (wt%) alloy were investigated through uniaxial tensile testing, scanning electron microscopy, and electron backscatter diffraction. The results showed that the alloy exhibited twinning-induced plasticity (TWIP) effect and significant work hardening behavior when the mean grain size ranged from 49 to 104 pm. However, when the alloy had heterogeneous grain structures and smaller grain sizes (d0 around 30 pm), the TWIP effect was absent and the alloy exhibited high yield strength but no work hardening.